Good point on the 4 wire vs. 2 wire. Our telephone wiring was originally only 2 wire and I had to splice the other pair in order to support 2 phone lines (a long time ago). That's why I could use the existing wiring to run the display and avoided a long, difficult, run of new cable. It was also made simple as the HW50C is in the same bay as the telephone jack and the display in in the same cabinet as an existing telephone jack.